🎲 Dice Expectation and Probabilities in Craps
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✅ What Is Dice Expectation?
Expectation (or expected value) is a mathematical concept that tells us the average result we can expect from a random event over time. In the case of dice, it’s the average value you would get if you rolled the dice thousands or millions of times.
For One Die:
- Possible outcomes: 1, 2, 3, 4, 5, 6
- Each has an equal probability:
- Expected Value (EV) =
For Two Dice (Used in Craps):
- Possible sums: 2 through 12
- Total combinations: 36 (6 sides × 6 sides)
- Some sums are more likely than others. For example:
- 7 can be rolled in 6 ways (e.g., 1+6, 2+5, 3+4, etc.)
- 2 or 12 only in 1 way each (1+1 or 6+6)
So, the expected value for a roll of two dice is:
That’s the average result you'd see over many rolls.
🎯 Probability Breakdown (Craps Focused)
Sum | Combinations | Probability |
---|---|---|
2 | 1 (1+1) | 1/36 ≈ 2.78% |
3 | 2 | 2/36 ≈ 5.56% |
4 | 3 | 3/36 ≈ 8.33% |
5 | 4 | 4/36 ≈ 11.11% |
6 | 5 | 5/36 ≈ 13.89% |
7 | 6 | 6/36 ≈ 16.67% |
8 | 5 | 5/36 ≈ 13.89% |
9 | 4 | 4/36 ≈ 11.11% |
10 | 3 | 3/36 ≈ 8.33% |
11 | 2 | 2/36 ≈ 5.56% |
12 | 1 (6+6) | 1/36 ≈ 2.78% |
These probabilities form the foundation of craps — the rules and payouts are structured around them.
🧠Conclusion: Do Dice Perform as Theory Predicts?
Yes — in the long run, dice perform very closely to what theory and probability predict. Here’s why:
- Randomness: Properly made and rolled dice are fair, meaning each side has an equal chance of landing.
- Law of Large Numbers: Over many rolls, the actual outcomes converge to the theoretical probabilities.
- For example, if you roll dice 36,000 times, you’ll see a 7 appear close to 6,000 times (about 16.67%).
Real-World Note:
Short-term deviations (like rolling a 7 five times in a row) are normal and expected in randomness — but over time, these balance out.
✅ Summary
- Dice expectation tells us what outcome we should expect on average.
- In craps, the most common total is 7, with an expected value of 7 for two dice.
- The probabilities of each dice combination are known and consistent.
- Over time, real dice rolls closely match theoretical expectations, confirming the reliability of mathematical models in games of chance like craps.
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